Amorphous poly(d,l-lactide) coating

ABSTRACT

Implantable devices formed of or coated with a material that includes an amorphous poly(D,L-lactide) formed of a starting material such as meso-D,L-lactide are provided. The implantable device can be used for the treatment, mitigation, prevention, or inhibition of a disorder such as atherosclerosis, thrombosis, restenosis, hemorrhage, vascular dissection or perforation, vascular aneurysm, vulnerable plaque, chronic total occlusion, patent foramen ovale, claudication, anastomotic proliferation for vein and artificial grafts, bile duct obstruction, ureter obstruction, tumor obstruction, or combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser. No. 11/117,813 filed on Apr. 29, 2005, the teaching of which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to coatings or implantable devices, such as stents or coatings on a stent, formed of a material that contains amorphous poly(D,L-lactide) (PDLLA) with a crystallinity of about or lower than 10%.

2. Description of the Background

Although stents work well mechanically, the chronic issues of restenosis and, to a lesser extent, stent thrombosis remain. Pharmacological therapy in the form of a drug-delivery stent appears a feasible means to tackle these biologically derived issues. Polymeric coatings placed onto the stent serve to act both as the drug reservoir, and to control the release of the drug. One of the commercially available polymer coated products is stents manufactured by Boston Scientific. For example, U.S. Pat. Nos. 5,869,127; 6,099,563; 6,179,817; and 6,197,051, assigned to Boston Scientific Corporation, describe various compositions for coating medical devices. These compositions provide to stents described therein an enhanced biocompatibility and may optionally include a bioactive agent. U.S. Pat. No. 6,231,590 to Scimed Life Systems, Inc., describes a coating composition, which includes a bioactive agent, a collagenous material, or a collagenous coating optionally containing or coated with other bioactive agents.

A current paradigm in biomaterials is the control of protein adsorption on the implant surface. Uncontrolled protein adsorption, leading to mixed layer of partially denatured proteins, is a hallmark of current biomaterials when implanted. Such a surface presents different cell binding sites from adsorbed plasma proteins such as fibrogen and immunogloblulin G. Platelets and inflammatory cells such as monocyte/macrophages and neutrophils adhere to these surfaces. Unfavorable events can be controlled by the use of non-fouling surfaces. These are materials, which absorb little or no protein, primarily due to their hydrophilic surface properties.

Another limitation of current drug-delivery stents stems from the fact that the stent is a foreign body. Use of drug-delivery stents has proved successful by use of controlled release of anti-proliferative or anti-inflammatory drugs to control restenosis. However, drug-delivery stents still have a small, but measurable, incidence of sub-acute thrombosis. Moreover, drug-delivery stents have not driven restenosis to zero levels, especially in more challenging patient subsets such as diabetics or patients with small vessels, and/or long, diffuse lesions. A biomaterials-based strategy for further improving the outcome of drug-delivery stents is by the use of biobeneficial materials or surfaces in stent coatings. A biobeneficial material is one which enhances the biocompatibility of a device by being non-fouling, hemocompatible, actively non-thrombogenic, or anti-inflammatory, all without depending on the release of a pharmaceutically active agent.

Poly(lactic acid) (PLA) is a bioabsorbable material with a long history of use. One of the negative aspects of using bioabsorbable material is late term inflammatory reactions. One of the reasons causing late term inflammatory reactions is a burst release of acidic degradation products at a late time point. Another cause is the release of polymer crystallites at a late time point once the amorphous polymer phase has degraded. It has been well documented that polymerization of D,L-lactic acid, and during degradation of the resulting polymers, can lead to the formation of stereocomplexes of PLA polymers. These stereocomplexes are the result of co-crystallization of enatiomerically pure poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) polymers or polymeric blocks (see, for example, Ikada, Y., et al., Macromolecules 20:904-06 (1987)). Studies have shown that these stereocomplexes have crystalline structures (see, for example, Okihara, T., et al., J. Macromol. Sci. Phys. B30(1/1):119-140 (1991); Tsuji, H., et al., Macromolecules 24:5651-6 (1991)). Accordingly, PLA formed by polymerization of D,L-lactic acids which allows for the formation of homologous sequences of L-lactic and/or D-lactic acid may cause late term inflammatory reactions. The present invention addresses such problems by providing a polymeric material for coating implantable devices.

SUMMARY OF THE INVENTION

Provided herein is a coating on an implantable device. The coating contains an amorphous PLA polymer formed of D-lactic acid and L-lactic acid, the polymer is not made from a 50/50 blend of L,L-lactide and D,D-lactide. The amorphous PLA polymer has a crystallinity of about 10% or lower, about 5% or lower, about 2% or lower, about 1% or lower, about 0.5% or lower, about 0.2% or lower, about 0.1% or lower, about 0.05% or lower, about 0.01% or lower, about 0.005% or lower, or about 0.0001%. The polymer defined herein can be used alone or in combination with another biocompatible polymer and/or a biobeneficial material to form coatings on implantable medical devices, or to form the implantable medical devices themselves. In some embodiments, the coatings or medical devices optionally include a bioactive agent. Some exemplary bioactive agents are paclitaxel, docetaxel, estradiol, nitric oxide donors, super oxide dismutases, super oxide dismutases mimics, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO), tacrolimus, dexamethasone, rapamycin, rapamycin derivatives, 40-O-(2-hydroxy)ethyl-rapamycin (everolimus), 40-O-(3-hydroxy)propyl-rapamycin, 40-O-[2-(2-hydroxy)ethoxy]ethyl-rapamycin, and 40-O-tetrazole-rapamycin, 40-epi-(N1-tetrazolyl)-rapamycin (ABT-578), pimecrolimus, imatinib mesylate, midostaurin, clobetasol, prodrugs thereof, co-drugs thereof, and combinations thereof. The implantable device can be implanted in a patient for the treatment, mitigation, prevention, or inhibition of a disorder such as atherosclerosis, thrombosis, restenosis, hemorrhage, vascular dissection or perforation, vascular aneurysm, vulnerable plaque, chronic total occlusion, claudication, anastomotic proliferation for vein and artificial grafts, bile duct obstruction, ureter obstruction, tumor obstruction, or combinations thereof.

DETAILED DESCRIPTION

Provided herein is a coating on an implantable device. The coating contains an amorphous PLA polymer formed of D-lactic acid and L-lactic acid, which is not made from a 50/50 blend of L,L-lactide and D,D-lactide. The amorphous PLA polymer has a crystallinity of about 10% or lower, about 5% or lower, about 2% or lower, about 1% or lower, about 0.5% or lower, about 0.2% or lower, about 0.1% or lower, about 0.05% or lower, about 0.01% or lower, about 0.005% or lower, or about 0.0001%. The polymer defined herein can be used alone or in combination with another biocompatible polymer and/or a biobeneficial material to form coatings on implantable medical devices, or to form the implantable medical devices themselves. In some embodiments, the coatings or medical devices optionally include a bioactive agent. Some exemplary bioactive agents are paclitaxel, docetaxel, estradiol, nitric oxide donors, super oxide dismutases, super oxide dismutases mimics, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO), tacrolimus, dexamethasone, rapamycin, rapamycin derivatives, 40-O-(2-hydroxy)ethyl-rapamycin (everolimus), 40-O-(3-hydroxy)propyl-rapamycin, 40-O-[2-(2-hydroxy)ethoxy]ethyl-rapamycin, 40-O-tetrazole-rapamycin, 40-epi-(N1-tetrazolyl)-rapamycin (ABT-578), pimecrolimus, imatinib mesylate, midostaurin, clobetasol, prodrugs thereof, co-drugs thereof, and combinations thereof. The implantable device can be implanted in a patient to treat or prevent a disorder such as atherosclerosis, thrombosis, restenosis, hemorrhage, vascular dissection or perforation, vascular aneurysm, vulnerable plaque, chronic total occlusion, claudication, anastomotic proliferation for vein and artificial grafts, bile duct obstruction, ureter obstruction, tumor obstruction, or combinations thereof.

Polymer crystallinity is generally used to define the morphology of a polymer. Crystalline state of a material can be defined in a number of different ways, e.g., density, enthalpy or free energy change on heating, spectroscopic associations, presence of certain planes of registry in microscopy for instance. For example, in the terms of XRD (x-ray diffraction), a crystal is defined as perfect 3-D order. Perfect 3-D order means that the structure repeats in all directions so that by describing the structure locally (in a repeating 3-d unit) the entire structure can be uniquely described. In a polymer, crystallinity reflects the presence in the polymer regions of three-dimensional order consisting of identical repeating units with the same orientation. The most direct evidence comes from x-ray diffraction studies where the sample displays one or more sharp diffraction peaks, although other methods such as determination of a melting point by DSC are also used. The crystallinity of a polymer is a function of polymer structure and intermolecular forces, e.g., hydrogen-bonding or van der Waal's forces, of polymer molecules. A good discussion of crystallinity in polymer is given at Odian, George, Principles of Polymerization, 3rd ed., John Wiley & Sons, New York, 1991, p. 27.

Formation of Amorphous PLA

The formation of stereocomplexes requires the presence of homologous sequences of L-lactic acid and D-lactic acid. Under a given set of conditions, e.g., temperature, pressure, solvent(s), and concentration, the presence of a higher degree of homologous sequences of L-lactide and D-lactide in a PLA polymer will generally cause the PLA to have a higher tendency to form stereocomplexes, generating a PLA polymer with a higher degree of crystallinity. Accordingly, to form a PLA polymer with a low degree of crystallinity, it is desirable to reduce the degree of homologous sequences of L-lactide and D-lactide in a PLA polymer.

PDLLA polymers are generally synthesized by polymerization of D,L-lactide using stannous octoate as the catalyst. There are three types of D,L-lactide, meso-D,L-lactide, racemic D,L-lactide, and blend-D,L-lactide (Formulae I-III):

In one embodiment of the present invention, the amorphous PLA polymer can be synthesized by polymerization of a meso-lactide (Scheme I):

Using meso-D,L-lactide, the greatest number of Ds or Ls in sequence is 2. Consequently, there are no homologous sequences with more than 2 Ds or Ls in the polymer.

In another embodiment, the amorphous PLA polymer can be synthesized by polymerization of racemic-lactide (Scheme II):

The distribution of the various combinations of D-lactide and L-lactide depends on the length of the polymer sequence, but is predictable with statistics. For example, in a sequence of eight (8) lactates, the distribution of all D or all L is given in Table 1.

TABLE 1 Distribution of D or L lactates in a eight(8) lactate sequence 2 in sequence (L-L/D-D): 12.5%,  4 in sequence (L-L-L-L/D-D-D-D): 50%, 6 in sequence (D-D-D-D-D-D/L-L-L-L-L-L): 25%, 8 in sequence (D-D-D-D-D-D-D-D/L-L-L-L-L-L-L-L): 12.5% 

In another embodiment of the present invention, the amorphous PLA polymer can be synthesized by polymerization of blend-D,L-lactide. According to distribution statistics, a blend of 50% D-lactide and 50% L-lactide has a distribution of 25% D,D-lactide, 50% meso-D,L-lactide, and 25% L-lactide (Formula III), which is essentially a mixture of meso-D,L-lactide and racemic-D,L-lactide. Therefore, the polymerization of blend-D,L-lactide will generate a PLA polymer having homologous sequences of lactates whose number and size in the polymer are between those of the PLA polymers from the polymerization of meso-D,L-lactide and racemic-D,L-lactide.

The D,L-lactides as used herein is cyclic lactides. Preparation of cyclic lactides are well documented in the art, and cyclic lactides are generally made by: (1) polycondensation of lactic acid to make a low MW poly(lactic acid), (2) depolymerization of the poly(lactic acid) by increasing the temperature and decreasing the pressure, and (3) distilling off the cyclic lactide formed.

meso-D,L-lactides can be isolated from the cyclic lactides made according to the procedures set forth above. The dipole moments of the D,D/L,L-lactides and the dipole moment of the meso-D,L-lactide are different. Accordingly, meso-D,L-lactide can be separated from D,D/L,L-lactides by conventional separation methods such as distillation, recrystallization, and/or chromatography.

The amorphous PLA polymer can be used to form an implantable device such as a stent or a coating on an implantable device such as a stent. In some embodiments, the amorphous PLA polymer can be used alone or in combination with another biocompatible polymer, optionally with a biobeneficial material and/or a bioactive agent.

Coating Constructs

In some embodiments, the poly(meso-D,L-lactide) (meso-DLPLA) can be used to modulate absorption rate in vivo for both a coating such as a coating formed onto a drug-delivery stent and a fully absorbable device such as a stent. The meso-DLPLA composition can range from about 5% to about 100% in the coating or the absorbable device. For example, the meso-DLPLA can be used in combination with racemic-poly(D,L-lactide) (racemic-DLPLA) to form a coating having any of the following construct schemes:

(1) blends of meso-DLPLA with racemic-DLPLA,

(2) a layer of meso-DLPLA as the outer layer and a layer of racemic-DLPLA as the inner layer or vice versa to modulate the absorption rate of the coating and/or to modulate the release rate of a drug, if any, and

(3) alternating the meso-DLPLA and the racemic-DLPLA.

Alternatively, the meso-DLPLA can be used with syndiotactic poly(L-lactide) (LPLA) to form a coating having any of the following construct schemes, each independently or in combination:

(1) blends of meso-DLPLA with LPLA,

(2) a layer of meso-DLPLA as the outer layer and a layer of LPLA as the inner layer or vice versa to modulate the absorption rate of the coating and/or to modulate the release rate of a drug, if any, and

(3) alternating the meso-DLPLA and the LPLA.

In some embodiments, the meso-DLPLA can form a composition with racemic-DLPLA to form a coating with LPLA having any of the following construct schemes, each independently or in combination:

(1) blends of LPLA with a composition that includes meso-DLPLA and racemic-DLPLA, and

(2) a layer that includes meso-DLPLA and racemic-DLPLA alternating with a layer that includes LPLA. The alternating structure can be applied either by coating the DLPLA or extruding.

In one embodiment, the meso-DLPLA can form a composition with poly(L-lactide-co-D,L-lactide) (LPLA-co-DLPLA) to form a coating with LPLA having any of the following construct schemes, each independently or in combination:

(1) blends of LPLA with a composition that includes meso-DLPLA and LPLA-co-DLPLA, and

(2) a layer that includes meso-DLPLA and LPLA-co-DLPLA alternating with a layer that includes LPLA.

Syndiotactic LPLA can be synthesized from meso-lactide by using a chiral catalyst (see, e.g., Ovit, T. M., et al., Stereochemistry of lactide polymerization with chiral catalysts: new opportunities for stereocontrol using polymer exchange mechanisms, J Am Chem Soc. 124(7):1316-26 (2002)).

The coating having meso-poly(D,L-lactide) can have a variety of beneficial properties. For example, inclusion of meso-poly(D,L-Lactide) increases the absorption rate of polymer matrix in the coating, and inclusion of meso-poly(D,L-Lactide) increases the water absorption of polymer matrix due to the absence of D-D-D or L-L-L blockyness in the polymer. Therefore, by varying the absorption rate and water absorption of the polymer matrix, one can modulate the release rate of a drug encapsulated within the polymer matrix. In addition, the increased absorption rate and water absorption of the polymer matrix allows the use of high MW starting material for relevant mechanical properties in certain applications.

Biocompatible Polymers Other than Meso-DLPLA

In some embodiments of the present invention, the meso-DLPLA can be used in combination with one or more additional biocompatible polymer which is not meso-DLPLA. The additional biocompatible polymer can be biodegradable (both bioerodable or bioabsorbable) or nondegradable, and can be hydrophilic or hydrophobic. Hydrophilic is defined to have a 6 (cal/cm)^(1/2) value (Hildebrand solubility parameter) greater than about 8.5 (cal/cm)^(1/2), e.g., a δ value of about 8.5 (cal/cm)^(1/2), about 9.5 (cal/cm)^(1/2), about 10.5 (cal/cm)^(1/2) or about 11.5 (cal/cm)^(1/2). The Hildebrand solubility parameter is a measure of the cohesive energy density, or polarity of a substance.

Representative biocompatible polymers include, but are not limited to, poly(ester amide), polyhydroxyalkanoates (PHA), poly(3-hydroxyalkanoates) such as poly(3-hydroxypropanoate), poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxyhexanoate), poly(3-hydroxyheptanoate) and poly(3-hydroxyoctanoate), poly(4-hydroxyalkanaote) such as poly(4-hydroxybutyrate), poly(4-hydroxyvalerate), poly(4-hydroxyhexanote), poly(4-hydroxyheptanoate), poly(4-hydroxyoctanoate) and copolymers including any of the 3-hydroxyalkanoate or 4-hydroxyalkanoate monomers described herein or blends thereof, poly polyesters, poly(D,L-lactide), poly(L-lactide), polyglycolide, poly(D,L-lactide-co-glycolide), poly(L-lactide-co-glycolide), polycaprolactone, poly(lactide-co-caprolactone), poly(glycolide-co-caprolactone), poly(dioxanone), poly(ortho esters), poly(anhydrides), poly(tyrosine carbonates) and derivatives thereof, poly(tyrosine ester) and derivatives thereof, poly(imino carbonates), poly(glycolic acid-co-trimethylene carbonate), polyphosphoester, polyphosphoester urethane, poly(amino acids), polycyanoacrylates, poly(trimethylene carbonate), poly(iminocarbonate), polyurethanes, polyphosphazenes, silicones, polyesters, polyolefins, polyisobutylene and ethylene-alphaolefin copolymers, acrylic polymers and copolymers, vinyl halide polymers and copolymers, such as polyvinyl chloride, polyvinyl ethers, such as polyvinyl methyl ether, polyvinylidene halides, such as polyvinylidene chloride, polyacrylonitrile, polyvinyl ketones, polyvinyl aromatics, such as polystyrene, polyvinyl esters, such as polyvinyl acetate, copolymers of vinyl monomers with each other and olefins, such as ethylene-methyl methacrylate copolymers, acrylonitrile-styrene copolymers, ABS resins, and ethylene-vinyl acetate copolymers, polyamides, such as Nylon 66 and polycaprolactam, alkyd resins, polycarbonates, polyoxymethylenes, polyimides, polyethers, poly(glyceryl sebacate), poly(propylene fumarate), poly(n-butyl methacrylate), poly(sec-butyl methacrylate), poly(isobutyl methacrylate), poly(tert-butyl methacrylate), poly(n-propyl methacrylate), poly(isopropyl methacrylate), poly(ethyl methacrylate), poly(methyl methacrylate), epoxy resins, polyurethanes, rayon, rayon-triacetate, cellulose acetate, cellulose butyrate, cellulose acetate butyrate, cellophane, cellulose nitrate, cellulose propionate, cellulose ethers, carboxymethyl cellulose, polyethers such as poly(ethylene glycol) (PEG), copoly(ether-esters) (e.g. poly(ethylene oxide/poly(lactic acid) (PEO/PLA)), polyalkylene oxides such as poly(ethylene oxide), polypropylene oxide), poly(ether ester), polyalkylene oxalates, polyphosphazenes, phosphoryl choline, choline, poly(aspirin), polymers and co-polymers of hydroxyl bearing monomers such as HEMA, hydroxypropyl methacrylate (HPMA), hydroxypropylmethacrylamide, PEG acrylate (PEGA), PEG methacrylate, 2-methacryloyloxyethylphosphorylcholine (MPC) and n-vinyl pyrrolidone (VP), carboxylic acid bearing monomers such as methacrylic acid (MA), acrylic acid (AA), alkoxymethacrylate, alkoxyacrylate, and 3-trimethylsilylpropyl methacrylate (TMSPMA), poly(styrene-isoprene-styrene)-PEG (SIS-PEG), polystyrene-PEG, polyisobutylene-PEG, polycaprolactone-PEG (PCL-PEG), PLA-PEG, poly(methyl methacrylate)-PEG (PMMA-PEG), polydimethylsiloxane-co-PEG (PDMS-PEG), poly(vinylidene fluoride)-PEG (PVDF-PEG), PLURONIC™ surfactants (polypropylene oxide-co-polyethylene glycol), poly(tetramethylene glycol), hydroxy functional poly(vinyl pyrrolidone), biomolecules such as collagen, chitosan, alginate, fibrin, fibrinogen, cellulose, starch, collagen, dextran, dextrin, fragments and derivatives of hyaluronic acid, heparin, fragments and derivatives of heparin, glycosamino glycan (GAG), GAG derivatives, polysaccharide, elastin, chitosan, alginate, and combinations thereof. In some embodiments, the polymer can exclude any one of the aforementioned polymers.

As used herein, the terms poly(D,L-lactide), poly(L-lactide), poly(D,L-lactide-co-glycolide), and poly(L-lactide-co-glycolide) can be used interchangeably with the terms poly(D,L-lactic acid), poly(L-lactic acid), poly(D,L-lactic acid-co-glycolic acid), and poly(L-lactic acid-co-glycolic acid), respectively.

Biobeneficial Material

The meso-DLPLA can form an absorbable device, or a coating, optionally with a biobeneficial material. The combination can be mixed, blended, or coated in separate layers. The biobeneficial material useful in the coatings described herein can be a polymeric material or non-polymeric material. The biobeneficial material is preferably non-toxic, non-antigenic and non-immunogenic. A biobeneficial material is one which enhances the biocompatibility of a device by being non-fouling, hemocompatible, actively non-thrombogenic, or anti-inflammatory, all without depending on the release of a pharmaceutically active agent.

Representative biobeneficial materials include, but are not limited to, polyethers such as poly(ethylene glycol), copoly(ether-esters) (e.g. poly(ethylene oxide/poly(lactic acid) (PEO/PLA)), polyalkylene oxides such as poly(ethylene oxide), poly(propylene oxide), poly(ether ester), polyalkylene oxalates, polyphosphazenes, phosphoryl choline, choline, poly(aspirin), polymers and co-polymers of hydroxyl bearing monomers such as hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), hydroxypropylmethacrylamide, poly(ethylene glycol)acrylate (PEGA), PEG methacrylate, 2-methacryloyloxyethylphosphorylcholine (MPC) and n-vinyl pyrrolidone (VP), carboxylic acid bearing monomers such as methacrylic acid (MA), acrylic acid (AA), alkoxymethacrylate, alkoxyacrylate, and 3-trimethylsilylpropyl methacrylate (TMSPMA), poly(styrene-isoprene-styrene)-PEG (SIS-PEG), polystyrene-PEG, polyisobutylene-PEG, polycaprolactone-PEG (PCL-PEG), PLA-PEG, poly(methyl methacrylate)-PEG (PMMA-PEG), polydimethylsiloxane-co-PEG (PDMS-PEG), poly(vinylidene fluoride)-PEG (PVDF-PEG), PLURONIC™ surfactants (polypropylene oxide-co-polyethylene glycol), poly(tetramethylene glycol), hydroxy functional poly(vinyl pyrrolidone), biomolecules such as albumin, fibrin, fibrinogen, cellulose, starch, collagen, dextran, dextrin, hyaluronic acid, fragments and derivatives of hyaluronic acid, heparin, fragments and derivatives of heparin, glycosamino glycan (GAG), GAG derivatives, polysaccharide, elastin, chitosan, alginate, silicones, PolyActive™, and combinations thereof. In some embodiments, the coating can exclude any one of the aforementioned polymers.

The term PolyActive™ refers to a block copolymer having flexible poly(ethylene glycol) and poly(butylene terephthalate) blocks (PEGT/PBT). PolyActive™ is intended to include AB, ABA, BAB copolymers having such segments of PEG and PBT (e.g., poly(ethylene glycol)-block-poly(butyleneterephthalate)-block poly(ethylene glycol) (PEG-PBT-PEG).

In a preferred embodiment, the biobeneficial material can be a polyether such as poly(ethylene glycol) (PEG) or polyalkylene oxide.

Bioactive Agents

The meso-DLPLA can form a absorbable device or a coating optionally with one or more bioactive agents. These bioactive agents can be any agent which is a therapeutic, prophylactic, or diagnostic agent. These agents can have anti-proliferative or anti-inflammatory properties or can have other properties such as antineoplastic, antiplatelet, anti-coagulant, anti-fibrin, antithrombonic, antimitotic, antibiotic, antiallergic, antioxidant as well as cystostatic agents. Examples of suitable therapeutic and prophylactic agents include synthetic inorganic and organic compounds, proteins and peptides, polysaccharides and other sugars, lipids, and DNA and RNA nucleic acid sequences having therapeutic, prophylactic or diagnostic activities. Nucleic acid sequences include genes, antisense molecules which bind to complementary DNA to inhibit transcription, and ribozymes. Some other examples of other bioactive agents include antibodies, receptor ligands, enzymes, adhesion peptides, blood clotting factors, inhibitors or clot dissolving agents such as streptokinase and tissue plasminogen activator, antigens for immunization, hormones and growth factors, oligonucleotides such as antisense oligonucleotides and ribozymes and retroviral vectors for use in gene therapy. Examples of anti-proliferative agents include rapamycin and its functional or structural derivatives, 40-O-(2-hydroxy)ethyl-rapamycin (everolimus), and its functional or structural derivatives, paclitaxel and its functional and structural derivatives. Examples of rapamycin derivatives include methyl rapamycin, ABT-578, 40-O-(3-hydroxy)propyl-rapamycin, 40-O-[2-(2-hydroxy)ethoxy]ethyl-rapamycin, and 40-O-tetrazole-rapamycin. Examples of paclitaxel derivatives include docetaxel. Examples of antineoplastics and/or antimitotics include methotrexate, azathioprine, vincristine, vinblastine, fluorouracil, doxorubicin hydrochloride (e.g. Adriamycin® from Pharmacia & Upjohn, Peapack N.J.), and mitomycin (e.g. Mutamycin® from Bristol-Myers Squibb Co., Stamford, Conn.). Examples of such antiplatelets, anticoagulants, antifibrin, and antithrombins include sodium heparin, low molecular weight heparins, heparinoids, hirudin, argatroban, forskolin, vapiprost, prostacyclin and prostacyclin analogues, dextran, D-phe-pro-arg-chloromethylketone (synthetic antithrombin), dipyridamole, glycoprotein IIb/IIIa platelet membrane receptor antagonist antibody, recombinant hirudin, thrombin inhibitors such as Angiomax ä (Biogen, Inc., Cambridge, Mass.), calcium channel blockers (such as nifedipine), colchicine, fibroblast growth factor (FGF) antagonists, fish oil (omega 3-fatty acid), histamine antagonists, lovastatin (an inhibitor of HMG-CoA reductase, a cholesterol lowering drug, brand name Mevacor® from Merck & Co., Inc., Whitehouse Station, N.J.), monoclonal antibodies (such as those specific for Platelet-Derived Growth Factor (PDGF) receptors), nitroprusside, phosphodiesterase inhibitors, prostaglandin inhibitors, suramin, serotonin blockers, steroids, thioprotease inhibitors, triazolopyrimidine (a PDGF antagonist), nitric oxide or nitric oxide donors, super oxide dismutases, super oxide dismutase mimetic, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO), estradiol, anticancer agents, dietary supplements such as various vitamins, and a combination thereof. Examples of anti-inflammatory agents including steroidal and non-steroidal anti-inflammatory agents include tacrolimus, dexamethasone, clobetasol, combinations thereof. Examples of such cytostatic substance include angiopeptin, angiotensin converting enzyme inhibitors such as captopril (e.g. Capoten® and Capozide® from Bristol-Myers Squibb Co., Stamford, Conn.), cilazapril or lisinopril (e.g. Prinivil® and Prinzide® from Merck & Co., Inc., Whitehouse Station, N.J.). An example of an antiallergic agent is permirolast potassium. Other therapeutic substances or agents which may be appropriate include alpha-interferon, pimecrolimus, imatinib mesylate, midostaurin, bioactive RGD, and genetically engineered epithelial cells. The foregoing substances can also be used in the form of prodrugs or co-drugs thereof. The foregoing substances are listed by way of example and are not meant to be limiting. Other active agents which are currently available or that may be developed in the future are equally applicable.

The dosage or concentration of the bioactive agent required to produce a favorable therapeutic effect should be less than the level at which the bioactive agent produces toxic effects and greater than the level at which non-therapeutic results are obtained. The dosage or concentration of the bioactive agent can depend upon factors such as the particular circumstances of the patient, the nature of the trauma, the nature of the therapy desired, the time over which the ingredient administered resides at the vascular site, and if other active agents are employed, the nature and type of the substance or combination of substances. Therapeutic effective dosages can be determined empirically, for example by infusing vessels from suitable animal model systems and using immunohistochemical, fluorescent or electron microscopy methods to detect the agent and its effects, or by conducting suitable in vitro studies. Standard pharmacological test procedures to determine dosages are understood by one of ordinary skill in the art.

Examples of Implantable Device

As used herein, an implantable device may be any suitable medical substrate that can be implanted in a human or veterinary patient. Examples of such implantable devices include self-expandable stents, balloon-expandable stents, stent-grafts, grafts (e.g., aortic grafts), artificial heart valves, patent foramen ovale closure devices, cerebrospinal fluid shunts, pacemaker electrodes, and endocardial leads (e.g., FINELINE and ENDOTAK, available from Guidant Corporation, Santa Clara, Calif.). The underlying structure of the device can be of virtually any design. The device can be made of a metallic material or an alloy such as, but not limited to, cobalt chromium alloy (ELGILOY), stainless steel (316L), high nitrogen stainless steel, e.g., BIODUR 108, cobalt chrome alloy L-605, “MP35N,” “MP20N,” ELASTINITE (Nitinol), tantalum, nickel-titanium alloy, platinum-iridium alloy, gold, magnesium, or combinations thereof “MP35N” and “MP20N” are trade names for alloys of cobalt, nickel, chromium and molybdenum available from Standard Press Steel Co., Jenkintown, Pa. “MP35N” consists of 35% cobalt, 35% nickel, 20% chromium, and 10% molybdenum. “MP20N” consists of 50% cobalt, 20% nickel, 20% chromium, and 10% molybdenum. Devices made from bioabsorbable or biostable polymers could also be used with the embodiments of the present invention. The device itself, such as a stent, can also be made from the described inventive polymers or polymer blends.

Method of Use

In accordance with embodiments of the invention, a coating or device of the various described embodiments can be formed on an implantable device or prosthesis, e.g., a stent. For coatings including one or more active agents, the agent will retain on the medical device such as a stent during delivery and expansion of the device, and released at a desired rate and for a predetermined duration of time at the site of implantation. In accordance with some other embodiments of the invention, bioabsorbable or non-degradable devices can be formed of a material containing the polymer of Formula I. The material can be the polymer of Formula I or a polymer blend containing the polymer of Formula I with one or more biocompatible polymers, optionally with a biobeneficial material and/or a bioactive agent, which are defined above.

Preferably, the medical device is a stent. The stent described herein is useful for a variety of medical procedures, including, by way of example, treatment of obstructions caused by tumors in bile ducts, esophagus, trachea/bronchi and other biological passageways. A stent having the above-described coating is particularly useful for treating occluded regions of blood vessels caused by abnormal or inappropriate migration and proliferation of smooth muscle cells, thrombosis, and restenosis. Stents may be placed in a wide array of blood vessels, both arteries and veins. Representative examples of sites include the iliac, renal, and coronary arteries.

For implantation of a stent, an angiogram is first performed to determine the appropriate positioning for stent therapy. An angiogram is typically accomplished by injecting a radiopaque contrasting agent through a catheter inserted into an artery or vein as an x-ray is taken. A guidewire is then advanced through the lesion or proposed site of treatment. Over the guidewire is passed a delivery catheter, which allows a stent in its collapsed configuration to be inserted into the passageway. The delivery catheter is inserted either percutaneously or by surgery into the femoral artery, brachial artery, femoral vein, or brachial vein, and advanced into the appropriate blood vessel by steering the catheter through the vascular system under fluoroscopic guidance. A stent having the above-described coating may then be expanded at the desired area of treatment. A post-insertion angiogram may also be utilized to confirm appropriate positioning.

EXAMPLES

The embodiments of the present invention will be illustrated by the following set forth prophetic examples. All parameters and data are not to be construed to unduly limit the scope of the embodiments of the invention.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications can be made without departing from this invention in its broader aspects. Therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit and scope of this invention.

Example 1 Synthesis of meso-poly(D,L-lactide)

To a 500 ml, 3-necked flask equipped with argon purge, vacuum line, short-path distillation head, and mechanical stirrer is added L-lactic acid (125 g, y mole), D-lactic acid (125 g, y, mole), and zinc oxide (5 g. Y mole). A vacuum of 100 mm Hg is applied, and the solution is heated with stirring at 140° C. for about 8 hours to form lactic acid oligomer while distilling off the water formed. The pressure is lowered to 2 mm Hg, and the solution temperature raised to about 210° C. to distill off the lactide formed by depolymerization, which consists of a 25/25/50 blend of L-lactide, D-lactide, and meso-D,L-lactide. The lactides formed are transferred to another 500 ml flask, and vacuum distilled at a pressure of 1 mm Hg to separate the racemic-D,L-lactide from the meso-D,L-lactide. The meso-D,L-lactide can also be separated from the racemic-D,L-lactide by recrystallization. In general, the racemic-D,L-lactide will crystallize more readily, leaving the meso-D,L-lactide in the mother liquor.

Example 2 Synthesis of poly(meso-D,L-lactide)

To a 250 ml, three necked flask, equipped with magnetic stirring, vacuum, and argon purge is added 1,6-hexanediol (14.77 g, 0.125 mole). Using an oil bath, the diol is heated to 60° C., and stirred under vacuum for two hours to remove water. The flask is purged with argon and the meso-D,L-lactide from Example 1 (108.0 g, 0.75 mole) is added. Vacuum is applied with stirring for another 30 minutes. After purging with argon, the flask is heated to 140° C., and polymerization initiated by addition of 10.8 ml of a 5% (w/w) solution of stannous octoate in dry toluene. After stirring for 24 hours, the reaction solution is cooled and poured into 500 ml of cold methanol to precipitate the polymer. The polymer is washed with methanol/petroleum ether and dried under vacuum.

Example 3 Stent Coating with poly(meso-D,L-lactide)

A medical article with two layers of coating can be fabricated to comprise everolimus by preparing a first composition and a second composition, wherein the first composition can be a primer layer comprising a matrix of a polylactide, and the second composition can be a matrix of a polylactide and an active agent. A first composition can be prepared by mixing the poly(meso-D,L-lactide) at 2% solids (w/w) in a 70/30 (w/w) blend of acetone/cyclohexanone. The first composition can be sprayed onto a surface of a bare 12 mm VISION™ stent (Guidant Corp.) (“example stent”), and dried to form a primer. An example coating technique comprises spray-coating with a 0.014 round nozzle, a feed pressure of about 0.2 atm and an atomization pressure of about 1.3 atm, applying about 20 μg of wet coating per pass until a wet coating weight of about 80 μg is reached, drying the coating at about 50° C. for about 10 seconds between passes and baking the coating at about 80° C. for about 1 hour after the final pass to form a dry primer layer with about 60 μg of solids. A second composition can be prepared by mixing poly(meso-D,L-lactide) with everolimus at a weight ratio of 1/2 with 2% (w/w) polymer solids in a 70/30 acetone/cyclohexanone blend. This solution is sprayed onto the primered stents and dried to form an agent layer coating. Spray-coating is performed with a 0.014 nozzle, a feed pressure of about 0.2 atm and an atomization pressure of about 1.3 atm, applying about 20 μg of wet coating per pass until a weight coating weight of about 190 μg is reached, drying the coating at about 50° C. for about 10 seconds between passes and baking the coating at about 50° C. for about 1 hour after the final pass to form a dry agent layer with about 167 μg of solids. 

1. A coating comprising an amorphous poly(D,L-lactide) (PDLLA) having a degree of crystallinity of about 10% or below, wherein the PDLLA is not made from a 50/50 blend of L,L-lactide and D,D-lactide.
 2. The coating of claim 1, wherein the amorphous PDLLA is prepared by polymerization of meso-D,L-lactide.
 3. The coating of claim 1, wherein the amorphous of PDLLA has a degree of crystallinity of about 1% or below.
 4. The coating of claim 2, comprising at least one additional biocompatible polymer.
 5. An implantable device comprising the coating of claim
 1. 6. (canceled)
 7. (canceled)
 8. The implantable device of claim 5, wherein the coating further comprises a biocompatible polymer and optionally a biobeneficial material, wherein the biocompatible polymer is selected from the group consisting of poly(ester amide), polyhydroxyalkanoates (PHA), poly(3-hydroxyalkanoates), poly(4-hydroxyalkanoates), polymers and copolymers comprising a monomer selected from the group consisting of 3-hydroxypropanoate, 3-hydroxybutyrate, 3-hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxyheptanoate, 3-hydroxyoctanoate, 4-hydroxybutyrate, 4-hydroxyvalerate, 4-hydroxyhexanote, 4-hydroxyheptanoate, and 4-hydroxyoctanoate, polyesters, poly(D,L-lactide), poly(L-lactide), polyglycolide, poly(D,L-lactide-co-glycolide), poly(L-lactide-co-glycolide), polycaprolactone, poly(lactide-co-caprolactone), poly(glycolide-co-caprolactone), poly(dioxanone), poly(ortho esters), poly(anhydrides), poly(tyrosine carbonates) and derivatives thereof, poly(tyrosine ester) and derivatives thereof, poly(imino carbonates), poly(glycolic acid-co-trimethylene carbonate), polyphosphoester, polyphosphoester urethane, poly(amino acids), polycyanoacrylates, poly(trimethylene carbonate), poly(iminocarbonate), polyurethanes, polyphosphazenes, silicones, polyesters, polyolefins, polyisobutylene and ethylene-alphaolefin copolymers, acrylic polymers and copolymers, vinyl halide polymers and copolymers, such as polyvinyl chloride, polyvinyl ethers, polyvinyl methyl ether, polyvinylidene halides, poly(vinylidene fluoride-co-hexafluoropropylene), polyvinylidene chloride, polyacrylonitrile, polyvinyl ketones, polyvinyl aromatics, polystyrene, polyvinyl esters, polyvinyl acetate, copolymers of vinyl monomers with each other and olefins, ethylene-methyl methacrylate copolymers, acrylonitrile-styrene copolymers, ABS resins, ethylene-vinyl acetate copolymers, poly(n-butyl methacrylate), poly(sec-butyl methacrylate), poly(isobutyl methacrylate), poly(tert-butyl methacrylate), poly(n-propyl methacrylate), poly(isopropyl methacrylate), poly(ethyl methacrylate), poly(methyl methacrylate), polyamides, Nylon 66 and polycaprolactam, alkyd resins, polycarbonates, polyoxymethylenes, polyimides, polyethers, poly(glyceryl sebacate), poly(propylene fumarate), epoxy resins, polyurethanes, rayon, rayon-triacetate, cellulose acetate, cellulose butyrate, cellulose acetate butyrate, cellophane, cellulose nitrate, cellulose propionate, cellulose ethers, carboxymethyl cellulose, polyethers, poly(ether-esters), poly(ethylene oxide-co-lactic acid) (PEO/PLA), polyalkylene oxides, poly(propylene oxide), polyalkylene oxalates, polyphosphazenes, phosphoryl choline, poly(aspirin), polymers and co-polymers of hydroxyl bearing monomers, hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), hydroxypropylmethacrylamide, PEG acrylate (PEGA), PEG methacrylate, 2-methacryloyloxyethylphosphorylcholine (MPC) and n-vinyl pyrrolidone (VP), carboxylic acid bearing monomers, methacrylic acid (MA), acrylic acid (AA), alkoxymethacrylate, alkoxyacrylate, and 3-trimethylsilylpropyl methacrylate (TMSPMA), poly(styrene-isoprene-styrene)-PEG (SIS-PEG), polystyrene-PEG, polyisobutylene-PEG, polycaprolactone-PEG (PCL-PEG), PLA-PEG, poly(methyl methacrylate)-PEG (PMMA-PEG), polydimethylsiloxane-co-PEG (PDMS-PEG), polypropylene oxide-co-polyethylene glycol, poly(tetramethylene glycol), hydroxy functional poly(vinyl pyrrolidone), glycosamino glycan (GAG), GAG derivatives, silicones, and combinations thereof.
 9. The implantable device of claim 8, wherein the biobeneficial material is selected from the group consisting of poly(ethylene glycol), poly(alkylene oxides), phosphoryl choline, 2-methacyloyloxyethylphosphoryl choline, poly(vinyl pyrrolidone), poly(styrene sulfonate), nitric oxide preserver, peptide amphiphile, pro-healing polymers, NO-donor polymers, hyaluronic acid, fibrin, albumin, elastin, dextran, dextrin, polysaccharides, heparin, fullerenes, and a combination thereof.
 10. The implantable device of claim 5, further comprising a bioactive agent.
 11. (canceled)
 12. The implantable device of claim 10, wherein the bioactive agent is selected from the group consisting of paclitaxel, docetaxel, estradiol, nitric oxide donors, super oxide dismutases, super oxide dismutases mimics, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO), tacrolimus, dexamethasone, rapamycin, rapamycin derivatives, 40-O-(2-hydroxy)ethyl-rapamycin (everolimus), 40-O-(3-hydroxy)propyl-rapamycin, 40-O-[2-(2-hydroxy)ethoxy]ethyl-rapamycin, and 40-O-tetrazole-rapamycin, ABT-578, pimecrolimus, imatinib mesylate, midostaurin, clobetasol, prodrugs thereof, co drugs thereof, and a combination thereof.
 13. (canceled)
 14. The implantable device of claim 5 which is a stent.
 15. (canceled)
 16. (canceled)
 17. An absorbable stent formed of a material comprising an amorphous poly(D,L-lactide) (PDLLA) having a degree of crystallinity of about or below 10%, wherein the PDLLA is not made from a 50/50 blend of L,L-lactide and D,D-lactide.
 18. The absorbable stent of claim 17, wherein the amorphous PDLLA is prepared by polymerization of meso-D,L-lactide.
 19. The absorbable stent of claim 17, further comprising at least one additional biocompatible polymer and optionally a biobeneficial material and/or a bioactive agent.
 20. (canceled)
 21. The absorbable stent of claim 17, further comprising a biobeneficial material and/or optionally a bioactive agent.
 22. (canceled)
 23. A method of treatment, mitigation, prevention, or inhibition of a disorder in a patient comprising implanting in the patient the implantable device of claim 5, wherein the disorder is selected from the group consisting of atherosclerosis, thrombosis, restenosis, hemorrhage, vascular dissection or perforation, vascular aneurysm, vulnerable plaque, chronic total occlusion, patent foramen ovale, claudication, anastomotic proliferation for vein and artificial grafts, bile duct obstruction, ureter obstruction, tumor obstruction, and combinations thereof.
 24. A method of treating a disorder in a patient comprising implanting in the patient the absorbable stent of claim 17, wherein the disorder is selected from the group consisting of atherosclerosis, thrombosis, restenosis, hemorrhage, vascular dissection or perforation, vascular aneurysm, vulnerable plaque, chronic total occlusion, patent foramen ovale, claudication, anastomotic proliferation for vein and artificial grafts, bile duct obstruction, ureter obstruction, tumor obstruction, and combinations thereof.
 25. An implantable device comprising a coating that comprises: (1) a layer of a blend of meso-DLPLA with racemic-DLPLA, (2) a layer of meso-DLPLA as the outer layer and a layer of racemic-DLPLA as the inner layer or a layer of racemic-DLPLA as the outer layer and a layer of meso-DLPLA as the inner layer, (3) alternating layers of the meso-DLPLA and of the racemic-DLPLA, or (4) a combination thereof.
 26. An implantable device comprising a coating that comprises: (1) a layer of a blend of meso-DLPLA with synditactic polylactide (LPLA), (2) a layer of meso-DLPLA as the outer layer and a layer of LPLA as the inner layer or a layer of LPLA as the outer layer and a layer of meso-DLPLA as the inner layer, (3) alternating layers of the meso-DLPLA and of the LPLA, or (4) combinations thereof.
 27. An implantable device comprising a coating that comprises: (1) a layer of a blend of LPLA with a composition including meso-DLPLA and racemic-DLPLA, (2) a layer that includes meso-DLPLA and racemic-DLPLA alternating with a layer that includes LPLA, or (3) a combination thereof.
 28. An implantable device comprising a coating that comprises: (1) a layer of a blend of LPLA with a composition including meso-DLPLA and LPLA-co-DLPLA, (2) a layer that includes meso-DLPLA and LPLA-co-DLPLA alternating with a layer that includes LPLA, or (3) a combination thereof. 